Capacitive distance sensor

ABSTRACT

A capacitive distance sensor is provided. The distance sensor includes a sensor element having an electrically conductive, elongated, flat sensor area which in turn contains a number of holes. The sensor area is completely surrounded by an electrically non-conductive insulating body, with the result that the insulating body completely covers the edge regions of the holes. The sensor element is produced, in particular, by first of all making the holes in the sensor area. In a subsequent step, the sensor area is completely encased by the insulating body which also completely fills the holes in the sensor area.

This nonprovisional application is a continuation of InternationalApplication No. PCT/EP2011/004454, which was filed on Sep. 5, 2011, andwhich claims priority to German Patent Application No. DE 10 2010 045008.1, which was filed in Germany on Sep. 10, 2010, and which are bothherein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a capacitive distance sensor having anelongated sensor element, in particular for use in the automobileindustry. Furthermore, the invention relates to a method formanufacturing such a sensor element.

2. Description of the Background Art

In the automobile industry such sensors are used, in particular, fordetecting an object approaching a vehicle or vehicle component, forexample as part of a parking aid or as part of an anti-trapping devicefor electrically adjustable windows or doors. A further field ofapplication of such capacitive distance sensors is aerospace or use inindustrial systems.

US 005166679A discloses a capacitive distance sensor having a sensorelement which comprises a sensor surface and which is mounted on anelement to be protected. The sensor surface is substantially a planar,extensive, thin and electrically conductive surface and forms anelectrode of a capacitor. An object which penetrates the area to bemonitored by the sensor serves as an opposing electrode of thecapacitor. When the object approaches the sensor element, thecapacitance of the capacitor formed between the sensor surface and theopposing electrode changes. The change in capacitance is measureddirectly and/or indirectly by means of electronics. The distance betweenthe object and the sensor element is determined by means of themeasurement data.

DE 602 05 520 T2, which corresponds to U.S. Pat. No. 6,879,250, andwhich discloses a further capacitive distance sensor having an elongatedsensor element. The sensor element is bonded here onto a bodywork partof a motor vehicle.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide acapacitive distance sensor having an elongated sensor element which canbe easily and securely attached to an object and which is notsusceptible to corrosion or soiling. Furthermore, the invention is basedon the object of specifying a particularly suitable method formanufacturing such a sensor element.

According to an embodiment of the invention, the capacitive distancesensor comprises an elongated sensor element which contains anelectrically conductive, elongated, flat sensor surface. A number ofholes are formed in the, in particular strip-shaped, sensor surface. Forexample, the holes serve to accommodate an attachment component such asa screw or a clip by means of which the sensor element can be attachedto an object, such as the bodywork of a motor vehicle. Such attachmentpermits comparatively rapid mounting of the sensor element. In order toprotect the sensor surface against mechanical or chemical damage, suchas for example influences of the weather, when the sensor element ismounted in the external region of the motor vehicle according to theinvention the sensor surface is surrounded completely by an insulatingbody. In this context, the edge regions of the holes are also enclosedby the insulating body so that no region of the sensor surface is incontact with the environment.

The geometry of all the holes of the sensor surface can be the same. Thecenter points of the holes are expediently located on a straight linewhich extends in the longitudinal direction of the sensor element. Inparticular, the holes of the sensor surface are embodied as elongatedholes, wherein the comparatively long axes of the elongated holes extendalong the longitudinal direction of the sensor surface. Owing to theseelongated holes, the sensor element permits high tolerances during thearrangement of the attachment component on the motor vehicle without theholes having to be reworked to accommodate the attachment componentduring the mounting process.

In an embodiment of the invention, the sensor element is flexible. Thesensor surface can be composed of copper and is expediently formed froma ribbon cable line. The insulating body is composed, for example,essentially of PVC. The insulating body is preferably cuboid and has, inparticular, a length between 10 cm and 200 cm, a width between 0.1 cmand 10 cm and a thickness between 0.1 mm and 20 mm.

In an unmounted state, the insulating body can completely fill the holesof the sensor surface. For example, in this case during the mountingprocess the screws which serve for attachment are screwed directly intothe insulating body. However, in one preferred embodiment a number ofcutouts are already provided in the insulating body, in particular foreasy mounting of the sensor element on an object. A cutout is generallyunderstood here to be a through-opening inside the insulating body. Theinsulating body preferably has precisely as many cutouts as the sensorsurface has holes. In each case precisely one of the cutouts istherefore arranged inside one of the holes, wherein the edge of thecutout is not in contact with the edge of the respective hole, with theresult that the sensor element is sealed off hermetically. The distancebetween the edge of the cutout and the edge of the associated hole isadvantageously essentially constant, with the result that thecross-sectional area of the cutout has the shape of the associated hole,wherein the surface content of the cross-sectional area is smaller thanthe size of the hole. The shape of all the cutouts is expediently thesame.

A termination which is connected to the insulating layer in a sealedfashion is located at at least one longitudinal end of the sensorelement. The termination is preferably composed of a melting adhesivebased on polyamide, in particular made of macromelt, and it is injectionmolded or cast onto the sensor element. The termination canalternatively be plugged onto the end of the sensor element and fused orbonded to the insulating layer in a seal-forming fashion. A contactpoint, at which the sensor surface is in contact with an electricalconnecting line, is preferably embedded in at least one of theterminations.

According to the inventive manufacturing method, the holes can firstlymade in the sensor surface. This can be done, for example, by punching.

In a subsequent working step, the sensor surface can be completelyenclosed by the insulating body, wherein the holes of the sensor surfaceare firstly filled by the insulating body. The insulating body can beprovided, for example, by encapsulating the sensor surface by injectionmolding. It would also be conceivable to laminate the sensor surface inbetween two plastic strips which are bonded or fused to one another inorder to form the insulating body and have a greater extent than thesensor surface and protrude completely beyond the edges of the sensorsurface.

In an embodiment of the method, in a further working step precisely onecutout is made, preferably punched, in the insulating body in each casein the region of each of the holes in such a way that the edge of eachcutout is not in contact with the edge of the associated hole, and thesensor element is thus hermetically terminated.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are not limitiveof the present invention, and wherein:

FIG. 1 is a schematic view of a capacitive distance sensor with anelongated sensor element, and

FIG. 2 shows a detail of the sensor element in a perspective view.

DETAILED DESCRIPTION

Corresponding parts are provided with the same reference symbols in allthe figures.

FIG. 1 is a schematic view of a capacitive distance sensor 2. Thedistance sensor 2 comprises an elongated, flexible sensor element 4,electronics 6 and a connecting line 8 which connects the sensor element4 electrically to the electronics 6. For example, the distance sensor 2is located inside a motor vehicle. In particular, within the scope of akeyless automatic starting system (Keyless-Go) the approaching of theparked motor vehicle by a person is monitored by means of the distancesensor 2. In one expedient application case, the sensor element 4 ismounted in the rear region of the motor vehicle, for example on the rearbumper 10. The longitudinal direction 12 of the sensor element 4suitably runs parallel to the wheel axes of the vehicle.

The electronics 6 supply the sensor element 4 with current and evaluatethe measurement data of the sensor element 4. In particular, on thebasis of a signal emitted by the distance sensor 2, the rear tailgate ofthe motor vehicle can be opened, with the result that the approachingperson does not have to perform any manual activity to open thetailgate.

FIG. 2 illustrates the sensor element 4 in more detail. As is apparentfrom the illustration, the sensor element 4 comprises an insulating body14 into which a sensor surface 16 is embedded in such a way that thesensor surface 16 is completely enclosed by the insulating body 14. Theinsulating body 14 bears in a positively locking fashion against thesensor surface 16, for example in order to avoid displacement of thesensor surface 16 with respect to the insulating body 14 and/or in orderto increase the stability of the sensor element 4. The sensor surface 16which is composed, for example, of copper is elongated and flat and is,in particular, in the shape of a strip. A number of holes 18 are punchedinto the sensor surface 16. The holes 18 are in the shape of anelongated hole, wherein the long axes of the elongated holes extendalong the longitudinal direction 12 of the sensor surface 16. The centerpoints of the holes 18 are located on a straight line which extends inthe longitudinal direction 12 of the sensor surface 16 and is locatedcentrally on the sensor surface 16.

The insulating body 14 which is composed, in particular, of PVC is inthe shape of a flat cuboid, wherein two surfaces are parallel to thesensor surface 16. The insulating body 14 has, for example, a length ofapproximately 63 cm, a width of approximately 3 cm and a thickness ofapproximately 0.2 cm. A cutout 20 of the insulating body 14 runs withineach hole 18 of the sensor surface 16. The shape of the cutouts 20corresponds essentially to that of the holes 18. The edge region 22 ofthe holes 18 is filled by the insulating body 14. In the mounted stateof the distance sensor 2, for example in each case a screw 24 can belocated within the cutouts 20, which screw 24 is used to attach thesensor element 4 to an object.

A termination 26 (FIG. 1) is located at one end of the sensor element 4.The body of the termination 26 is composed of macromelt and is cast ontothe sensor element 4. A connecting point 28, at which the sensor element4 is electrically in contact with the connecting line 8, is embedded inthe termination 26.

The holes 18 are firstly punched into the sensor surface 16 within thecourse of the manufacture of the sensor element 4. In a subsequentworking step, the sensor surface 16 is encased completely by theinsulating body 14. The cutouts 20 are subsequently formed in theinsulating body 14.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are to beincluded within the scope of the following claims.

What is claimed is:
 1. A capacitive distance sensor comprising: a sensor element that comprises an electrically conductive, elongated, flat sensor surface, a plurality of holes formed in the sensor surface; and an electrically nonconductive insulating body completely enclosing the sensor surface such that the insulating body completely covers edge regions of the holes.
 2. The capacitive distance sensor as claimed in claim 1, wherein the holes are configured as elongated holes and wherein comparatively long axes of the elongated holes extend in a longitudinal direction of the sensor surface.
 3. The capacitive distance sensor as claimed in claim 1, wherein the sensor element is flexible.
 4. The capacitive distance sensor as claimed in claim 1, wherein the sensor surface is composed of copper.
 5. The capacitive distance sensor as claimed in claim 1, wherein at least a portion of the insulating body is composed of PVC.
 6. The capacitive distance sensor as claimed in claim 1, wherein the insulating body contains a plurality of cutouts corresponding to the plurality holes, and wherein each cutout extends within one of the holes.
 7. The capacitive distance sensor as claimed in claim 6, wherein a cross-sectional area of each cutout has substantially a same shape as that of the respective corresponding hole through which the cutout extends.
 8. A method for manufacturing a sensor element for a capacitive distance sensor as claimed in claim 1, the method comprising: forming a plurality of holes in the flat, elongated sensor surface, composed of the electrically conducive material; completely enclosing, in a subsequent working step, the sensor surface by an insulating body which is composed of an electrically nonconductive material and which also completely fills the holes of the sensor surface.
 9. The method for manufacturing a sensor element as claimed in claim 8, wherein, in a subsequent working step, a plurality of cutouts corresponding to the plurality of holes is made in the insulating body such that each cutout runs within one of the holes, and wherein an edge of the cutout is consistently at a distance from an edge of an associated hole. 